This application relates to a method to impart permanent stain resistance to textile fibers.
Both natural and synthetic fibers are easily stained during normal use. In fact, it has been estimated that more textile fibrous products, including clothing and carpeting, are discarded because they are stained or soiled than because the fibers are worn out.
Staining, as opposed to soiling, typically occurs when an exogenous colored material binds either ionically or covalently to the fiber. The ability of a staining material to bind to a fiber is a function of the type of active functional groups on the fiber and the staining material. For example, nylon fiber consists of polyamide polymers that have terminal carboxyl and (often protonated) terminal amino groups. Common household acid dyes (colored materials with negatively charged active groups), found in a number of materials, for example, wine, red colored soft drinks, and mustard, often form strong ionic bonds with the protonated terminal amine functions of nylon, resulting in discoloration of the nylon fiber.
A number of processes and treatments have been developed to protect nylon fiber from staining materials that attach to the terminal amine functions. The most widely used method involves the application to the polyamide fiber of a colorless aromatic formaldehyde condensation polymer (sometimes referred to below as a "novolac resin") that has sulfonate groups on the aromatic rings. The negatively charged sulfonate groups bind ionically to available protonated amino groups in the polyamide fiber, preventing the protonated amino groups from later binding to common household acid dyes. The polymeric coating also protects the carpet fiber by creating a barrier of negative electric charge at the surface of the fiber that prevents like-charged acid dyes from penetrating the fiber.
Examples of aromatic-formaldehyde condensation polymers are described in a number of patents, including U.S. Pat. No. 4,501,591 to Ucci, et al., and U.S. Pat. Nos. 4,592,940 and 4,680,212 to Blythe, et al (that describe a formaldehyde condensation product formed from a mixture of sulfonated dihydroxydiphenylsulfone and phenylsulphonic acid, wherein at least 40% of the repeating units contain an -SO.sub.3 X radical, and at least 40% of the repeating units are dihydroxydiphenylsulfone). U.S. Pat. No. 4,822,373 to Olson, assigned to Minnesota Mining and Manufacturing Company, describes a method for treating nylons for stain resistance, as well as fibrous products produced thereby, that includes treating the fiber with a mixture of a partially sulfonated novolac resin and polymethacrylic acid, copolymer of methacrylic acid, or combination of polymethacrylic acid and copolymers of methacrylic acid. U.S. Pat. No. 4,937,123 to Chang describes and claims a method for imparting stain resistance to nylon fibers that includes contacting the fibrous material with a solution that includes polymethacrylic acid, or a copolymer of methacrylic acid that includes at least 30 weight percent methacrylic acid, or combinations thereof, wherein the lower 90 weight percent has a weight average molecular weight in the range of 2500 to 250,000 and a number average molecular weight in the range of 500 to 20,000, and wherein the treated fibrous substrate has a resistance to staining of at least 5 (when measured against a scale of 1 to 8, with 1 indicative of no stain resistance and 8 indicative of excellent stain resistance).
U.S. Pat. No. 4,940,757 to Moss, et al., and assigned to Peach State Labs, Inc., describes a stain resistant composition for nylon fibers that is prepared by polymerizing an o-substituted acrylic acid in the presence of a novoloid resin.
Sulfonated aromatic formaldehyde condensation products marketed as stain resistant agents include Erional=NW (Ciba-Geigy Limited), Intratex N.TM.(Crompton & Knowles Corp.), Mesitol=NBS (Mobay Corporation), FX-369 (Minnesota Mining & Mfg. Co.), CB-130 (Grifftex Corp.), and Nylofixan P (Sandoz Chemical Corp.) Antron Stainmaster.TM. carpet manufactured by Du Pont contains nylon fibers that have both a fluorocarbon coating and a sulfonated phenolformaldehyde condensation polymeric coating.
Cotton fiber is a unicellular, natural fiber composed of almost pure cellulose, a carbohydrate with a large proportion of free hydroxyl groups. Cellulose is also a chief component in rayon (a manufactured fiber composed of regenerated cellulose, in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups), acetate (cellulose acetate fibers, in which the hydroxyl groups are partially acetylated), and triacetate (cellulose fibers in which at least 92% of the hydroxyl groups are acetylated). Colored material that can ionically or covalently bind to free hydroxyl groups in the cellulose will easily stain cotton fiber.
While application of stain treatments have improved the resistance of the above-mentioned fibers to certain colored materials, all of the treatments have the distinct disadvantage that they are not permanent because they are bound to the fiber by ionic, and not covalent, bonds. They are removed from the fiber after a number of shampooings. Therefore, after a time period, the fibrous product is just as susceptible to staining as before treatment. This is a very significant problem for commercial grade carpet, that must be cleaned very often.
It is therefore an object of the present invention to provide textile fibers, in particular polyamide and cellulosic fibers, that are permanently stain resistant.
It is another object of the present invention to provide a method to impart permanent stain resistance to textile fibers, and in particular to polyamide and cellulosic fibers.